Dynamic SLAs Discussion Omer Rana, School of Computer Science, Cardiff

Requirements Limitations of a single agreement –Modifications since agreement was in place Cost of doing re-establishment –Not fully aware of operating environment Flexibility in describing Service Level Objectives –Not sure what to ask for (not fully aware of the environment in which operating)

What is a “Dynamic Agreement” Case 1: Static Agreement –Identify Service Description Terms, –Guarantee Terms, and –Service Level Objectives (SLOs) Case 2: Dynamic Agreement –Identify Service Description Terms, –Guarantee Terms: defined as ranges or as functions –Service Level Objectives: defined as ranges or as functions

EU-Catnets

Cat-COVITE markets and Catallactic Agents for Query Services

Cat-COVITE for Data Mining Services

SLA Compliance (WS-QoC)

SDS has two primarily functions: SLA activation and SLA termination.  SLA activation  SLA termination Verify SLADistribute SLOSLA QoC Service Receipt SLA Deployment

MS is responsible for monitoring service invocations, detecting any violation of service level objectives and sending action guarantees to responsible parties. MS Architecture: propagates the obligations between the Subcomponents and control the interaction between them. maintains run-time information on the metrics that are part of the SLA. Compares measured SLA parameters against the thresholds defined in the SLA and notify the Action Service.. Notifies the responsible parties. Monitoring Service

Its role is to update the QoC metrics associated with a set of services. For each QoS metric, the QoC service computes the difference between the predicted or suggested value, and the actual value delivered. We can therefore consider the SLA to be a set: SLA = {m 1,...,m k } of metrics that need to be satisfied. Compute QoC Receipt from SDS Service Broker QoC

The projected value m p is the value that the service consumer and provider have agreed upon, and is defined in the SLA. The actual value m a is the value that the service provider delivers, and is measured by the monitoring service In the context of an SLA, therefore, we can determine ∆M for the i th metric (1 < i < k) – leading to: This normalised value allows us to ensure that we can fairly compare (within some limited bound) different metrics. A positive value occurs when the actual value is less than the projected value, and vice versa. Computing QoC

Not all metrics are likely to be of the same significance to a user. we can prioritize each metric – and therefore also the difference observed for that metric (between the actual and the predicted values). This leads us to the concept of a weighted (by !i) normalised difference for a given metric, hence: Computing QoC … 2

1.How can trust information be acquired based on interaction between service users and providers 2.How can trust information be used in the context of service composition (such as a workflow session) SLA Usage

Rating the Reliability of a service (cont..). ►A service user rates service behaviour by examining the terms in the SLA with his observation during service execution. ►As users cannot monitor the service execution directly, users compute the estimated execution time t est. The Rating Phase (cont..) ∆t = t gen - t est Time Difference Actual Execution Time Estimated Time Elements of a SLA

Rating the Reliability of a service. ►A user sends a service request to invoke a particular service. The Rating Phase Service Negotiate SLA SLA SLA established Invoking the service based on SLA SLA Violation ►SLA violation implies that the service was not executed successfully. RMS ►The user sends feedback to the RMS. ►The feedback is one the following values: { -2, -1, 0, 1, 2}

Series 1: Standard Download Series 2: With Trust Rating Simulation: 7 services 2 clients 100 downloads One shot downloads

Time Slot = 1 minute interval